>> If your old venti is intact, I don't see the need to copy it (or is it >> on the drive with the damaged fossil and you don't trust the drive?). > > If your venti disk is similar to the failed disk and of same > vintage, it is also likely to fail and should be replaced > before it actually does. Similarly replace all disks in a > RAID if one of the disks dies (and the death was not in the > first few months of its life).
our experience has been this is not a cost-effective way of dealing with disk failures as disks do not fail en masse. also, once a failure has occured, it is too late. if there are other disks with latent errors, raid reconstruction will fail. in a raid 5 array, a latent error + failed disk means that block can't be reconstructed. i think this corelation gives people the false impression that they do fail en masse, but that's really wrong. the latent errors probablly happened months ago. our solution to this problem (RaidShield™) is to preemtively scan disks while the raid is idle and rewrite these blocks. this either (a) corrects the bit rot (b) causes the drive to remap the sector or (c) notifies the user that there's a real disk problem so it can be replaced before a second drive in the array fails. - erik
